Production of pure caprolactam



United States Patent Ofi tice 3,35%,393 Patented Oct. 31, 1967 with liquid capro 3 350 393 PRonUcTioN or PUTRE CAPROLACTAM mndensatlon Norbert Petri and Hugo Strehler, Ludwigshafen (Rhine), baflles Germany, assignors-to Badische Anilin- & Soda-Fabrik Aktiengesellschaft, Ludwigshafen (Rhine), Rhineland, 5 An advantage of this Pfalz, Germany is used in fluidized con N0 Drawing. Filed 0d. 19, 1965, S61. N0. 498,136 gas m xture by means Claims priori application Germany, Oct. 31, 1964, reactlon chamber 15 m B 60 11 Claims. (Cl: 260239.3) has not been Separated ABSTRACT OF THE DESCLOSURE In a process for coverting c caprolactam by contactin at 210 450 C. and c efi'luent reaction gas, th gas with liquid caprolac yclohexanone oxime into g the oxime with a solid catalyst ondensing caprolactam from the e steps of quenching the reaction am having a temperature at least of cycloh The production of c subsequent vided with process is that when the catalyst f dust from the which flows air or water which has been preheated to temf ii gi' i g gg ggfg g ggg i g s 5 13152 135; & i l? thls thefgae oxide, 15 to 25% of phosphoric acid on silica gel are suitor a empem 0 up 0 able Silica gel aluminum oxide (which may be calcined) C., only gradually reaches the condensation temperature or Uranium dloxrde have proved to be Suitable as of h laetam upon entering the cooler so that m the riers The catalysts may be stationary or fluidized portion of the cooler in which condensation begins, but in In order to carry out the process accordl-eng to thrs which t Wan of the cooler is not yet covered by a Vention, the gas mixture leaving the reaction chamber is descending film of caprolactam, thermal decomposition of quenched by capmlactam at a temperature of from about the caprolactam takes place to a certain extent Apart to C preferably from about 0 to c from the consequent decrease in yield, purification of the either by passirrg the gas mixture into caprolactam eapcrrelaetam 18 made more dlmcult by the deeomposltlon at the said temperature for example into the bottom of pro nets fofmed Moreover Pertleularly e an Inert the column used for condensation, or by spraying caprocariier gas is used in the rearrangement reaction, only an lactam into the gas mlxture The difference between the incompiete condensation o the caprolactam is achieved temperature of the gaseous caprolactam to be quenched so that It may be necessary to attach to the e cooler a and that of the liquid lactam used for coolin should second cooler charged with cold water or brine In this therefore be at least 0 C but preferably a than prior art type of condensation, fairly large amounts of by- C. It is expedient to use the liquid caprolactam arisin products formed me rearrrengement alweys remam from the subsequent condensation column The liquid the lactam from the first cooling stage, which lower the lactam may also be Sprayed m the form of a Jet of liquld quality of the crude lacta m and make its purrficatio more 50 or in finely divided form into the gas mixture leaving the difiicult. The proportion of byproducts which are more reacrron Chamber The amount of lacram sprayed m Volatile than Capt 0130mm for example unsaturated should be at least sutficient to ensure that if the whole of mles anddwateg 2 g the laetam m it is vaporized the gas mixture is cooled to the desired i e00 f e W 1e may e lnecessary so temperature. It IS advantageous however to use a larger t at P eatfon is e even more e amount or" liquid caprolactam for example 3 to parts It 1s an ob ect of this invention to provide a new procby Weight, preferably about to parts by Weight of ess tor the recovery of caprolactam from hot vapors lactam for each part by weight of gas mixture to be eontammg eaProlaetam by Whleh the amount of byprod' quenched. After the gas mixture has been quenched it is ucts formed during condensation 1S considerably reduced advantageously passed upwardly into a column Provided and eonseqpenfly the quality of caprolaetlam 15 Improved 60 with bafiles for condensation. Packed columns, bubble Another ob ect of the invention is to provide a p ocess for tray Columns and vapor barfie plate columns are examples the recovery of Caprolaetam from hot vapors contammg of columns which may be used. The condensation as well caprolactam which enables condensation to be carried as the rearrangement may effected at armosphenc out a Operation These and other oblects a superatmospheric or subat'mospheric pressure and in the vantages will be better understood from the following depresence or absence of Inert gas The pressure used In tailed descnptloncondensation may differ from that used in rearrange- We have now found that in the production of caproment w quenchmg rs carried out by spraying m or lactam by catalytic rearrangement of cyclohexanone oxime lmectlng h 1 m th quenched vapor is preferably in contact with solid catalysts at elevated temperature in passed i h bottom or the lower thrrd of the column the presence or absen fm t g s, ap r r pr l m Condensation takes place in the column because a temperature gradient by adding a lo W boiling point liq is constantly maintained in the column uid, for example an each part by weight of vapor supplied. The low boiling point liquid not only results in a temperature gradient in the column, but also causes additional purification of the caprolactam, because volatile impurities are entrained by the vapor. The temperature conditions in the column are advantageously adjusted so that the caprolactam flows to the bottom, to which also the liquid lactam formed by quenching is led or in which the quenching is carried out, the volume being kept constant by continuous withdrawal of an appropriate amount thereof.

The proportion of byproducts remaining in the lactam depends on the bottoms temperature and the temperature of the first trays in the column. At the lower temperaures, the proportion of byproducts is greater than at the higher temperatures. It is advantageous to choose a temperature of from 180 to 250 C. at the point at which the quenched vapor is introduced into the column and a temperature of from 150 to 250 C. on the first trays in the column above the said point. The number of theoretical trays in the column should be such that no appreciable amount of lactam are contained in the vapor leaving the top of the column.

The invention is further illustrated by the following examples. The permanganate titration number (PTN) used in the following examples as a characteristic of the degree of purity is defined as follows:

Permanganate titration number, PTN for short, is the amount in milliliters of 10 N potassium permanganate solution used up by a solution of 1000 g. of caprolactam in 2500 g. of aqueous sulphuric acid before the permanganate color is stable for two minutes in a titration carried out at room temperature.

EXAMPLE 1 38.45 kg. of cyclohexanone oxime having a water content of 6% is rearranged to caprolactam in a fluidizedbed reactor 2000 mm. in length and 100 mm. in diameter at a temperature of 356 to 360 C. and a pressure of 280 mm. Hg in the course of 315 minutes in contact with 21.1 kg. of catalyst which is passed by means of air locks through the reaction chamber during the said period. The catalyst consists of aluminum oxide of boron oxide, has a particle size of 0.2 to 0.5 mm. and is kept in fluidized condition by 1.1 cu. m. (STP) per hour of nitrogen together with the vapors of oxime and lactam. The gas leaving the reaction chamber passes to a cyclone heated to 277 C. to separate dust and is then introduced into the bottoms (consisting of caprolactam which has already been condensed) of an uninsulated vapor bafile plate column having ten trays and having a diameter of 100 mm. The volume of bottoms is kept constant at 45 cc. by an overflow. 6.4 liters of water is added to the top tray of the column during the period of operation to condense caprolactam. The temperatures are as follows:

C Bottoms 200 First tray 190 Third tray 175 Fifth tray 95 Eighth tray Top of column 55 Condensed caprolactam fiows away over the bottom trays and through the bottoms, while the remaining gas mixture escapes at the top of the column. 33.54 kg. of crude lactam having an average PTN of 7500 is obtained.

Distillation of this lactam at 14 mm. Hg gives only 0.12%

by weight of water and byproducts at up to 140 C.

If, for comparison, the above procedure is repeated but condensation is carried out by a prior art method by 5 passing the gas leaving the reaction chamber, for dust separation, through a cyclone heated to 280 C., passing the caprolactam through a ball cooler having a length of 1000 mm. and filled in the lower half by 5 x 5 mm. coils of wire mesh of V2A-steel, through which water heated to C. is flowing, and condensing any residues of lactam from the gas in a subsequent cooler fed with water at 15 C., a crude lactam is obtained having an average PTN of 10,500. Distillation of this lactam at 14 mm. Hg gives 3.4% by weight of water and byproducts 15 at up to 140 C.

EXAMPLE 2 14.21 kg. of cyclohexanone oxime having a water content of 5% is rearranged to caprolactam in the fluidizedbed reactor described in Example 1 at 358 to 360 C. and a pressure of 785 mm. Hg in the course of 125 minutes in contact with 7.4 kg. of catalyst which is passed (by means of air locks) through the chamber in the said time. The catalyst is the same as in Example 1 and is kept in fiuidization by 3.36 cu. m. (STP) per hour of nitrogen and the vapors of oxime and lactam. The gas leaving the reaction chamber passes through a cyclone heated to 270 C. to remove dust and is passed into the bottoms (consisting of already condensed crude lactam) of the vapor baffie plate column described in Example 1.

' kept at 60 cc. by an over- The volume of the bottoms 1S fiow. The gas quenched in the bottoms then passes into the column into which 1.2 liters of water is introduced at the uppermost tray during the period of operation to efiect condensation of the caprolactam. The temperatures are as follows:

Bottoms 200 First tray 195 40 Third tray 170 Fifth tray 86 Eighth tray 72 Top of the column 70 The condensed caprolactam runs away as described in Examples 1. 12.61 kg. of crude lactam is obtained having an average PTN of 5700. Distillation of this lactam gives only 0.12% by weight of water and byproducts at up to 140 C. at 14 mm. Hg.

If the same procedure be followed, except that the gas leaving the reaction chamber is passed for dust separation through a cyclone heated to 345 C. and the caprolactam is condensed in two coolers, a crude lactam is obtained having an average PTN of 12,300. Distillation of this lactam at 14 mm. Hg gives 3.0% by weight of water and byproducts at up to 140 C.

55 EXAMPLE 3 15.72 kg. of cyclohexanone oxime having a water content of 4.7% is rearranged to caprolactam in the fluidizedbed reactor described in Example 1 at 360 C. and a pressure of 820 mm. Hg in the course of 117 minutes in contact with 7.1 kg. of catalyst passed during this period through the reaction chamber by means of air locks. The catalyst has the same composition as in Example 1, but the particle size is 0.5 to 1.0 mm.; it is kept fluidized by 5.5 cu. m. (STP) per hour of nitrogen and the oxime and lactam vapors. The gas leaving the reaction chamber passes, for dust separation, through a cyclone heated to 325 C. and is passed into the bottoms consisting of already condensed crude lactam of a column having a length of 1600 mm. and a diameter of 60 mm. which is filled with 8 x 8 mm. coils of VZA-steel wire mesh. The volume of the bottoms is kept at 165 cc. by an overflow. The gas which has been quenched in the bottoms then passes into the column into which 3.8 liters of water is introduced during the operational period at the top of EXAMPLE 4 During the course of 141.5 hours, 3072.5 kg. of hexanone oxime having a water content of 5.7%

The condensed caprolactam flows away as described 11 Example 1. 2703.3 kg. of crude lactam is obtained having an average PTN of 3500. Distillation of this lactam at 14 mm. Hg gives 0.3% by weight of water and byproducts at up to 140 C.

EXAMPLE 5 18.88 kg. of cyclohexanone oxime having a water content of 5% is rearranged to caprolactam in tre fluidizedbed reactor described in Example 1 at 358 to 360 C. and a pressure of 847 mm. Hg during the course of 160 heated to 330 C. in which three tubes of metal having a total filtering surface of 0.71 sq. m. are provided and is then introduced into the bottoms consisting of already condensed crude lactam in the vapor bafiie plate column described in Example 1. The volume of the bottoms is kept at 100 cc. by an overflow. The gas which has been quenched in the bottoms is then passed upwardly into the column to which during the operating period 3160 cc. of ethanol is added to the top tray of the column to condense the caprolactam. The temperatures are as follows:

C. Bottoms 205 First tray 140 Third tray Fifth tray 57 Eighth tray 50 Top of the column 50 The condensed caprolactam leaves as described in EX- ample 1. 16.34 kg. of crude lactam is obtained having an mm. Hg gives of only 0.2%

We claim:

water and byproducts in a total amount by weight at up to C.

of said gas mixture leaving the to maintain a temperature gradient over said condensation zone.

2. A process as claimed in claim 1 boiling solvent is Water.

3. A process as claimed in claim 1 wherein 3 to 60 parts by weight of lactam is used for quenching each part by weight of gas mixture.

4. A process as claimed in claim 2 wherein the amount of water added is 0.06 to 0.7 part by weight for each part by weight of vapor supplied.

5. A process as claimed in claim 1 which the condensation is formed by a column provided with =baflles.

6. A process as claimed in claim 1 carried out at a pressure of 10 to 500 mm. Hg.

7. A process as claimed in claim 1 wherein the caprolactam used for quenching has a temperature of about C. to 220 C.

8. A process as claimed in claim 3 wherein the amount of lactam used is 10 to 40 parts by weight.

9. A process as claimed in claim 4 wherein said amount of water is 0.2 to 0.4 part by weight.

10. A process as claimed in claim 5 wherein the quenched vapor is introduced into said column for said condensation at a temperature of 180 C. to 250 C.

11. A process as claimed in claim 10 wherein the low 3,154,539 10/1964 Irnich 260239.3 3,210,338 10/1965 Huber et a1. 260239.3

WALTER A. MODANCE, Primary Examiner. R. T. BOND, Assistant Examiner. 

1. IN A PROCESS FOR THE CONVERSION OF CYCLOHEXANONE OXIME INTO CAPROLACTAM BY CONTACTING SAID OXIME WITH A SOLID CATALYST IN A REACTION ZONE AT A TEMPERATURE OF 210*C. TO 450*C. AND CONDENSING CAPROLACTAM FROM THE GAS MIXTURE LEAVING THE REACTION ZONE, THE IMPROVEMENT WHICH COMPRISES: QUENCHING SAID GAS MIXTURE LEAVING THE REACTION ZONE WITH LIQUID CAPROLACTAM HAVING A TEMPERATURE OF ABOUT 70*C. TO 260*C. BUT AT LEAST 10*C. LOWER THAN THE TEMPERATURE OF SAID GAS MIXTURE LEAVING THE REACTION ZONE; AND CONDENSING THE CAPROLACTAM FROM SAID GAS MIXTURE IN A CONDENSATION ZONE BY DIRECT COOLING WITH A LOW BOILING SOLVENT INTRODUCED AT THE TOP OF SAID CONDENSATION ZONE IN AN AMOUNT SUFFICIENT TO MAINTAIN A TEMPERATURE GRADIENT OVER SAID CONDENSATION ZONE. 